1. Field of the Invention
The present invention relates to a piezoelectric inkjet printhead. More particularly, the present invention relates to a piezoelectric inkjet printhead having a temperature sensor for sensing the temperature of ink in an ink channel, and a method of making the same.
2. Description of the Related Art
In general, an inkjet printhead is a device that prints an image of a predetermined color by ejecting fine ink droplets onto a desired position of a recording medium. Inkjet printheads may be roughly classified into two types of printheads, based on the method of ink ejection. One of the two types of printheads is a thermally-driven type inkjet printhead, which generates a bubble in ink using a heat source and ejects ink using the force of expansion of the bubble. The other type is a piezoelectric inkjet printhead, which operates through the shape transformation of a piezoelectric element and ejects ink using pressure applied to the ink by the transformation of the piezoelectric element.
FIGS. 1 and 2 illustrate partial plan and sectional views, respectively, of a conventional piezoelectric inkjet printhead. Referring to FIGS. 1 and 2, the printhead may include a channel forming plate having a manifold 12 and a plurality of pressure chambers 16, which may be coupled to each other by a plurality of restrictors 14. The printhead may also include a plurality of nozzles 18.
An ink channel may include the manifold 12, a restrictor 14, a pressure chamber 16 and a nozzle 18. In detail, the manifold 12 may serve as a passage supplying ink flowing from an ink storage region (not shown) to each of a plurality of pressure chambers 16, and the plurality of restrictors 14 may serve as passages connecting the manifold 12 with the plurality of pressure chambers 16. The plurality of pressure chambers 16, which fill with ink to be ejected, may be arranged on one side or both sides of the manifold 12.
A plurality of piezoelectric actuators 40 may be provided on the channel forming plate 10. As an individual piezoelectric actuator 40 is driven, it causes a corresponding pressure chamber 16 to change its volume, thereby creating a pressure change for ejecting ink, or for inducing the inflow of ink to the pressure chamber 16 from the manifold 12. A portion of the channel forming plate 10 that constitutes an upper wall, or ceiling, of the pressure chamber 16 may serve as a vibrating plate 20, which is vibrated by driving the piezoelectric actuator 40. The channel forming plate 10 may be manufactured by processing a plurality of thin plates, e.g., silicon wafers, metal plates, synthetic resin plates, etc., to form the features making up the ink channels, and then stacking these plates.
Each piezoelectric actuator 40 may include a lower electrode 41, a piezoelectric element 42, and an upper electrode 43 sequentially stacked on the channel forming plate 10. A lower electrode insulation layer 31 may be formed between the lower electrode 41 and the channel forming plate 10. The lower electrode 41 may be formed on an entire surface of the lower electrode insulation layer 31 to serve as a common electrode for multiple piezoelectric actuators 40. The piezoelectric element 42 may be formed on the lower electrode 41 such that the piezoelectric element 42 is positioned above the corresponding pressure chamber 16. The upper electrode 43 may be formed on the corresponding piezoelectric element 42 to serve as a drive electrode for applying a voltage across the piezoelectric element 42.
To apply a drive voltage to the piezoelectric actuator 40 having the above-described structure, the upper electrode 43 may be connected to a flexible printed circuit (FPC) 50 for voltage supply. The FPC 50 may include a plurality of drive signal lines 51, where individual drive signal lines 51 are bonded to individual upper electrodes 43.
In operation, when the vibrating plate 20 is transformed by driving the piezoelectric actuator 40, the volume of the pressure chamber 16 reduces, which generates a pressure change in the pressure chamber 16 so that ink contained in the pressure chamber 16 is ejected to the outside. Subsequently, when the vibrating plate 20 is restored to an original shape by driving of the piezoelectric actuator 40, the volume of the pressure chamber 16 increases, which generates a pressure change, i.e., a negative pressure change, in the pressure chamber 16, so that ink flows from the manifold 12 into the pressure chamber 16 through the restrictor 14.
When the temperature of ink changes, the viscosity of the ink may also change. If the viscosity of the ink increases, the flow resistance of the ink may also increase, and thus the volume and ejection speed of an ink droplet ejected through the nozzle 18 may be reduced. Therefore, overall ink ejection performance may be reduced and satisfactory printing quality may not be obtained. Accordingly, it may be desirable to provide appropriate compensation for increased ink viscosity by raising the temperature of the ink through heating, or by raising the driving voltage applied to the piezoelectric actuator 40.
To manage this compensation, it may be desirable to accurately sense the temperature of the ink inside the inkjet printhead. However, it may not be straightforward to directly install a temperature sensor for sensing the temperature of ink in the inkjet printhead.